I am studying how the Satellite Based Augmentation System (SBAS) or the Ground Based Augmentation System (GBAS) affect the Instrument Approach Procedures, and I noticed that in ICAO's Aircraft Operations manual (8168, Volume II) it states:

Part III, Section 3, Chapter 5, 5.3.1: "General. In the intermediate approach segment any sensor can be used; however, the transition to the SBAS navigation shall be made 3.7 km (2.0 NM) prior to the FAF.

Part III, Section 3, Chapter 5, 5.3.2: Alignment. The intermediate approach segment of an SBAS procedure shall be aligned with the final approach segment.

Part III, Section 3, Chapter 6, 6.3.2: "The intermediate approach segment of a GBAS procedure shall be aligned with the final approach course."

Does the above quotes imply that the intermediate segment must be aligned with the final segment 2.0NM prior to the FAF, in order for the aircraft to be able to switch to SBAS navigation?

In addition, concerning both SBAS and GBAS, I would like to make sure if the rule concerning the alignment of the intermediate segment with the final segment implies that the whole segment (each leg of the intermediate segment) has to be aligned with the final, rather than only the last leg.

Could someone point me in the right direction?


1 Answer 1


I've never seen an SBAS approach that had more than one intermediate segment. In all cases, the IAF/IF is aligned and more than 2 NM from the FAF. There may be multiple IAFs that feed directly to the IAF/IF. A good example is the PSM RNAV (GPS) RWY 16:

PSM GBAS Approach

As you can see, ITAWA is aligned with PUDYE. You can get to ITAWA via SATAN, ITAWT, or directly. Arriving directly at ITAWA requires flying the procedure hold to establish the final approach course.

GBAS (or GLS in the US) is intended as a functional replacement for ILS and as such one of the goals is that GLS mimics the behavior of an ILS. As a result, the GLS procedures are designed to be flown just like an ILS approach.

You can compare the GLS and ILS approaches to Newark Rwy 04L below:


If you compare the two, you'll see the path from the FAF HOWYA to the MAP is identical. The IFs are slightly different as the GLS IF EMBAY is a pure extension of the glide path out to 2800 elevation. The ILS path is slightly different vertically between the IF and FAF due to having to identify the IF via the DME.

  • $\begingroup$ Gerry thank you for the indication that SBAS approach's intermediate segment consists of one leg. I have edited the question in order to include the GBAS navigation, could you comment on that too? $\endgroup$ Jun 28, 2019 at 16:53
  • $\begingroup$ @Gerry Did you use the Portsmouth approach because you thought you saw a PUDYE cat? I did. Hehe. $\endgroup$
    – wbeard52
    Jun 28, 2019 at 23:07
  • $\begingroup$ I’m just surprised someone named a waypoint SATAN $\endgroup$
    – TomMcW
    Jun 30, 2019 at 3:05
  • 1
    $\begingroup$ @wbeard52 IDEED. $\endgroup$
    – Gerry
    Jun 30, 2019 at 11:25
  • 1
    $\begingroup$ KILMA is an intersection and an IF for the ILS/LOC approach. Note that it's on the same radial to CRI as EMBAY. That's because the ILS/LOC does not expect any RNAV capability. Since the GLS approach is an RNAV procedure, it expects RNAV capability on the part of the aircraft. With an RNAV system, you don't need that IF transition. I expect there's an RNAV SID that transitions at EMBAY. $\endgroup$
    – Gerry
    Jul 2, 2019 at 18:45

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .